High and low burner gun flue coke oven with waste gas recirculation and decarbonizing air



J1me 1955 D. w. BONNETT 3,19

HIGH AND Low BURNER GUN FLUE COKE OVEN WITH WASTE GAS RECIRCULATION AND DECARBONIZING AIR. Filed Oct.19, 1961 3 Sheets-Sheet l a a a 'u 'INV'ENTOR 8 1/1 M? JbNa/er'l? r roam/s 7f D. w. BONNETT June 29, 1965 3,192,134-

HIGH AND LOW BURNER GUN FLUE COKE OVEN WITH WASTE GAS RECIRCULATION AND DECARBONIZING AIR Filed Oct. 19, 1961 5 Sheets-Sheet 2 Ig/EN TOR. I 241x051. M mills 5 7".

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D. W. BONNETT June 29, 1965 HIGH AND LOW BURNER GUN FLUE COKE OVEN WITH WASTE Filed Oct. '19. 1961 GAS RECIRCULATION AND DECARBONIZING AIR oup asg Iuqum Mums I Daniel W. Bennett, Pittsburgh, Pa.,

United States Patent HIGH AND LOWBURNER GUN COKE OVEN WITH WASTE GAS RECIRCULATION AND DE- CARBONIZING AIR f assignor to Koppel-s Company, Inc., a corporation of Delaware Filed Oct. '19, 1961, Ser. No. 146,229

4 Claims. (Cl. 202-241) 'The present invention relates to improvements in gas gun regenerative coke ovens having two sets of vertical combustion flues and two gun flues in each heating wall for operation in alternation with each other for upflow combustion and downflow of combustion products, and designed for rich gas underfiring with waste gas recirculation. More particularly, the invention relates to ovens 'of this type having a double divided vertical flue system in each heating wall with high and low burners in each flue, to provide uniform heating from top to bottom of the heating walls alongside the adjacent coking chambers.

The invention is especially designed for high ovens in which the distribution of the heat of rich fuel gas to the tops of the flues is diflicult when fuel gas of high calorific value is used for the underfiring fuel gas, such as the coke oven gas which is given off by the carbonization of coal in the oven chambers, due to the fact that they burn 1y, waste gas recirculation is taking place in the'gun flues with a short intense flame and deposit free carbon in the 'gun flues and high and low burners, unless diluted with recycled waste gases of combustion to produce a leaner fuel gas mixture, like blast furnace or producer gas. These gases burn with a longer flame of lesser intensity. The

rich fuel gas when diluted with waste gases also burn 'with a longer flame of lesser intensity and do not clog the gas gun flues and burners with free carbon.

It has been the practice to provide for decarbonization of the gun flues and burners, while they are off combustion, with air from outside the battery, to eliminate the clogging of the gun flues and burners when using rich fuel gas as the fuel gas for the underfiring, or alternatively it has also been the practice to recirculate waste gases "of combustion from inside the battery to the rich fuel 'gas while on flow'through the' gun flues and burners, to eliminate the clogging with free carbon and "to provide an elongated flame of lesser intensity, like that obtained as aforesaid with blast furnace or producer gas for the the tops of the flues and coal charges in the adjacent coking chambers is and has been diflicult, and 'to do this without clogging of the gun flues and low and high burners with free carbon during'the on operation of such gun flue-s,

burners, when undeniring these ovens With rich fuel gas,

such as coke oven or like fuel gas.

Accordingly, this is accomplished by providing a recirculation duct at each of the opposite ends of each pair "of gun flues in each heating wall at the level of the tops of the regenerators'. Each duct connects the gun flues for one of the two sets of vertical combustion flues in each heating wall with the top of the regenerator that is communicably connected for inflow of air and out flow especially for high ovens where the uniform heating of of waste gas to the other set of combustion flues in the same heating wall. Thus,,in each reversal period of operation of the two sets ofregenerators, vertical flues, and

.gun flues, the gunflues for'the updraft sets of vertical flues in the heating walls are connected to receive waste .for dilutions of the rich gas from a regenerator operable for all the updraft flues while air circulation is taking place in the gun flues for all the downdraft vertical combustion flues. This combination involving merely a simple short duct at the pusher and coke side end of each heating wall in a battery of horizontal coking retort ovens keeps the rich fuel gas feed system free of carbon. The concurrent waste gas recirculation lessens the tendency for carbon formation and the decarbonizing air assists in eliminating it if and when it might form. The air for decarbonizing is hot from the waste gas regenerators so that an improvement in fuel economy results, since no cold air is used for decarbonizing and, as no cold air is used, the gas guns on the-outside of thebattery which feed the gun flues remain at a more stable temperature. Decarbonizing air from outside the battery can be entirely eliminated when the draft in the off gun flue is'suflicient to draw enough air from an inflow air regenerator through the venturi used to aspirate the waste gas into the gun flue when it is on. This would make the decarbonization by air automatic and eliminate the need for air piping to attain the decarbonization.

The invention is not limitedin all its aspects to the double divided heating flue system, nor high ovens, nor high burners, since much of the advantage of the system' of simple recirculation ducts at the end of the heating Walls is also useful with single divided heating flue systems as well as multiplex systems of single and double hairpin flues, low ovens, with only low burners.

'versely of a battery of horizontal coking chambers on the line II of FIGURE 2;

FIGURE 2 is a composite vertical cross-sectional view taken longitudinally of the batteryon the lines A -A and B-B of FIGURE 1; V 4

FIGURE 3 is a composite horizontal sectional view taken on the lines DD, E-E and F-F of'FIGURE 2.

The same reference characters indicate the same parts in each of the several views of the drawings. Referring to the drawings, there is shown an upper longitudinal row of alternate horizontal coking chambers 10 and intermediate heating walls 11, each constituted of a row of vertical combustion or flame flues Y12, and :a lower row of alternate regenerators 14 and intermediate pillar walls 13 with the regenerator chambers in the form of j through regenerators 14 parallel to and below the coking 6O chambers 10, :and the pillar walls 13 beneath the heating ';12 for operation in alternation with each other as two sets for concurrent on inflow preheating of to, and off outflow of the waste gases of combustion from the heating flues 12. The heating flues 12 also operate as two sets in alternation for'concurrent on upflow combustion in one set and otf down-flow of the hot Waste gases of combustion from the flues in the other set. For this, each heating wall 11 is provided with'horizontal flow duct means in the form of two end to end horizontal lines 28 separated by a Wall 29 at the longitudinal median line of the battery. Each horizontal flue 28 is located at the top of the row of vertical ifiues 12. Each horizontal fiue 28-connect-s an exterior quarter group of fiues 12a with an interior quarter group of fiues 12b on the pusher sidelQand 12c and 12a on the coke side 20 halves of the battery. This forms the two sets of .on and off flues for each heating wall in which the flow may be on upflow in the quarter group 12a, 1120 in alternation with simultaneous oil downfiow of the hot waste gases of combustion in the other quarter group of tlues 12b, 12d, in accordance With the well-known reversal in operation of-the two. sets of regenerators. The alternate regenerators M are connected by the ducts 27 to operate as one of the sets of regenerators with two of the quarter groups in each half of :a heating wall that are. not connected with each other by a horizontal flue 2-8 in each of two adjacent heating vwallsand the intermediate regenerator-s N are likewise connected by the ducts 27 to operate as the other set of regenerators with the'remaining two quarter groups of lines that are not interconnected with each other by a horizontal flue 28 in each of two adjacent heating Walls.

Each heating wall 11 is also provided with two gun liues 30, 31 which extend throughout the entire length of the heatingwalls in the capitals 32 of the pillar walls 13, which capitals form the base or bottoms of the heating Walls 11 and their ilues '12. One gun flue 31 in each heating wall communicates by low 26a and high 261) burner rich gas riser ducts 26 with two of the quarter groups of flues 12 of one set and the other gun flue 31 in each heating wall communicates by low 26a and high 261) burner rich gas riser ducts 26 with the two other quarter groups of. lines 12 that form the other. set of heating .flues.

For combined recirculation of hot waste gases of combustion during on flow in the gun 'flues fat), 3.1 and burner.

ducts 26 and concurrent decarbonization with hot regeneratively preheated air of the gun lines 31), 3'1 and burner ducts 2.6 when idle to flow of rich fuel gas during off flow, a single recirculation duct, '17, 18, is provided at each of the opposite ends 19 and 26 of the heating walls 11 in the capitals 32. The recirculation ducts 17 at the pusher side 19 connect a gun flue 31 with a regenerator 14 that is connected byregenerator ducts 27. with the two quarter groups of dues 12'that are fed with rich fuel gas .by the other gun flue 30 through its low and high rich gasriser. ducts 26. The recirculation ducts 18 at the coke side 20 connect :a gun due 3% with a regenerator 14 that is connected by the regenerator ducts 27 with the two quarter groups 12a, 120 that are fed with rich fuel gas by a gun flue 31. V

- Air for combustion of rich gas in the heating fiues is supplied through air valves 22 to a regenerator reversal flow box 23 for each regenera-tor. This box also contains a valve 23' for exhaust of waste gas to a waste heat flue 24,iwhich leads to a smoke stack, not shown. The reversal boxes 23 communicate, each through a port 25, with one end of the sole fiues 47. As shown, a pair of sole fiues 47 are provided for each regenerator chamber. These sole lines each communicate through calibrated orifices in its top with the filler mass of the regenerator to discharge the air to be preheated thereunto and to with' draw waste gases of combustion off from the bottom of the regenerative filler mass in alternation in accordance wvith the well-known reversal in operation of regenerative .tops by horizontal flow ducts means 2h for operation of the fiues of each wall in quarter groups, for concurrent operation of an exterior quarter group 12a and an interior quarter group .120 as on combustion lines in alternation with an interior group 12b and an exterior group 12d as oil waste gas combustion products lines. In operation in alternation the gases from the two on groups during any one reversal tendto divide equally and pass in equal amounts to two concurrently operable off groups in a wall without the need for a partition wall 29. But due to the taper of the oven chambers,- which increase in width from the pusher side to the coke. side, to facilitate the pushing out of the finished coke cakes from the oven chambers, the coke side requires more heat units than the pusher side half because the coal mass is thicker, so that the partition walls 29 are of greater advantage in dividing the flow of gases to provide such greater volume of heat on the coke side half, without also providing partitions in the through regenerator chambers.

Regeneratively preheated air and non-regeneratively preheated rich fuel gas is supplied to the two exterior and two interior quarter groups of vertical flame flues'in alternation. This is attained by operating the regencrators as two sets {or concurrent on and off operation in alternation with each other, with alternate regenerat-ors M as one set for on and off operation inalternation with the intermediate regenerators N as the other set for concurrent off and on operation. This is done by connecting the conventional reversing mechanism,- not shown, for operating the valves 22, 23 for the flow reversal boxes 23 to open the air valves 22 and close the waste heat valve 23', for alternate regenerators M whileclosing the air valve 22 and opening the waste heat valve 23' for the intermediate regenerators N in one half of each 25 to 30 minutes, regenerative cycle, and then close the air valves 22 and open the waste heat valves 23' for the alternate regenerators M and open the air valves 22 and close the waste heat valves 23 forthe intermediate regenerators N for the next half of each regenerative cycle.

The intermediate regenerators M are each communically connected by regenerator ducts 27 with the pusher side exterior quarter group of fiues 12a and coke side interior quarter group of flues of alternate heating walls and with the pusher side interior quarter group of fines 12b and the coke side exterior quarter group of flues 12d of the intermediate heating walls on opposite sides of the coking chambers 10 above the alternate regenerators M. Y

The alternate regenerators N-are likewise communicably connected by regenerator ducts 27 with the pusher side exterior quarter group of fiues and 'coke side interior quarter group of flues of intermediate heating walls and with the pusher side interior quarter group of flucs .and the coke side exterior quarter group of flues of the alternate heating walls on opposite sides of the coking chambers 10 above the intermediate regenerators.

The rich fuel gas is fed to the vertical heating fiues 12 by metal gas guns at 15 and 16 through two gas gun flues 3%, 31 for each wall, guns 15 entering from the pusher side 19 and the other guns 16 entering from the coke side 20 of the battery. The two gas gun flues 3Q, 31 each extend along the bases of the heating walls 11 in the capital 32 of the pillar walls 13 and are connected by the gas risers 26 in such manner that each gun fine 30, 31 communicates only with the inner quarter group of flues nearest the side of the battery at which its gas gun enters, skips the outer quarter group of fiues on that side of the battery, skips the inner quarter group on the opposite side of the battery, and communicates with the exterior quarter group of fiues on the opposite side of the battery, to terminate at the outer recirculation duct 17 or 18 atthe outer endof the heating wall, so that each end flue is not fed with rich gas by'a metal gun in the region of the venturi 21. where the gas pressure is low due to the jet action of the. feed. gas. Only one of these gas gun fiues 30 or 31 is active at any one time so that only alternate groups of vertical flues in each heating wall are fed with rich fuel gas on one reverse by one of the gun flues 30, 31.

The reversal of operation of the gun lines 30, 31 for each heating wall 11 is effected by conventional reversgas from the rich fuel gas mains 34.

The drafts in the individual vertical flues 12 are regulated by sliding bricks 35 located in the horizontal flues 28 which are adjustable through the access passages .36 in the, oven roof through which coal. to be coked is charged into the tops of the coking chambers through coal charging holes 37 in the oven roof 38.

In operation, conventional reversing; mechanism, not shown, is set to operate air and Waste heat valves for all alternate regenerators M to open their air valves 22 and close their waste heat valves 23' and to concurrently close the air valves 22 and open the waste heat valves 23 for all intermediate regenerators N.

At this time, the reversing mechanism operates the rich gas supply valves 33, onthe pusher side 19 to the metal guns at 15 for gun flues 31 to close the valves 33 to the gun fiues 31 for all the intermediate heatingwalls and open the valves 33 to the metal guns 15 for gun flues 31' for all the alternate heating walls. At this time, the reversing mechanism also operates the rich gas supply ,valves 33 on the coke side 20, to opentall the valves 33 to the metal guns 16 for the gun flues 30 for all the intermediate heating walls and to close the .valves 33 to the metal guns 16 for gun flues 30 for all the alternate heating walls.-

Air from the alternate through regenerators M flows through regenerator ducts 27 to the vertical heating flues of the pusher side 19 interior groups of flues of the alternate heating walls M and the pusher, side 19 exterior group of flues of the intermediate heating walls N, as wall as to the coke side 20 exterior groups of flues in .the

alternate heating walls M and the coke side 20 interior groups of flues in the intermediate heating walls The gas and air then pass through the rich gas riser ducts 26 and regenerator airducts 27 to enter the pusher side exterior and coke side interior groups o f flues in the intervmediate heating Walls wherein they burn. The waste I gases of combustion flow through the horizontal flues 28 to, and down through the pusher side interior and coke side exterior groups of flues to leave through their regenerator ducts 27 and pass out to the two waste heat flues 24 through the intermediate regenerators N and .sole flues 47. Similar upflow combustion occurs in the pusher side interior and coke side exterior groups of flues in the alternate heating walls M, the hot waste gases of combustion flowing down through the pusher side exterior and coke side interior groups of flues in the alternate heating Walls to the intermediate regenerators N their sole flues 47 and two' waste heat tunnels or flues 24.

On reversal, the flow is in the reverse direction through the intermediate regenerators N and up through the groups ofiflues connected thereto and down through the flue groups connected to the alternate regenerators M to the waste heat tunnels. w I

During such reversals in operation, there is no inflow of fuel gas to through conduits 30, 31 conduits while their flues 12 are passing waste gas down through their ducts 27 to the regenerators M or N, since'they'are cut off from the gas mains 34 by the valves 33. However, air is drawn in through these conduits at their time from the tops of on regenerators through the recirculation ducts flowing along in the conduits or gun flues 30, 31 to the low and high rich gas riser burners for the flues. The combined actions of waste gas dilution and decarbonizing aeration in thegun flues and high and low burner risers during their on and off operations insures continuity of unclogged lines and elongation of the flames to the tops of the heating flues 12. The tops of the regenerators can be readily seen clear through the battery through the peep t holes 18' and cleaned when necessary from this vantage point. The waste gas leaves the regenerators through two sole flue channels and two waste heat flues which permits build- 10 inglnew'higher ovens on old foundations having two such Waste heat flues 24, and Without requiring metal lined sole flues 47 to prevent loss of air pressure for the flues'to the waste heat sole channels 47, as is disclosed in my copending application'Sen'al No. 146,163, filed 15 October 19, 1961, entitled Double Divided Gun Flue Horizontal Coking Retort Oven.

The novel gas gun flue decarbonizing air and waste gas recirculation feature for the aforesaid double divided heating flue system is also equally applicable to compart- 20 'mentalized regenerator chamber sections individualized to end to end reverse flow groups of flues, and is also equally applicable to rich gas conduit systems for single divided and hairpin flue heating systems along the heating Walls. The invention as hereinabo've. set forth is embodied 'in a particular form and manner'but may be variously embodied within the scope of the claims as hereinafter made. i

I claim:

1. In a coking retort oven, a horizontal heating wall constituted of two sets of vertical combustion flues each operable in alternation with the other for upflow combustion and downflow of combustion products, said flues each having a regenerator air inlet port at its bottom for inflow of regeneratively preheated air thereto from a re- 35 generator and for outflow of waste gases ofcombustion from the flue to said regenerator, a pair ofhorizontal rich fuel gas gun flues operable in alternation with each other for inflow of rich fuel gas, said gun flues extending lengthwise of the heating wall at the botto-rnof said 4J3 flues, with rich fuel gas riser ducts leading from one of thetwo gun flues to the bottoms of the flues of one set, and with rich fuel gas riser ducts leading from the other of the .two gun flues to the bottoms of the flues of the other set, a waste gas recirculation duct atteach of the opposite ends of the horizontal heating walls,

one of said waste gas recirculation ducts connecting one of said gun flues with a regenerator, which regenerator is operable for inflow of air while said one gun flue is idle to flow of rich fuel gas -to its set of vertical flues and the other of the two gun flues is in operation for inflow of rich gas to its set of vertical flues, and which fregenera'tor is operable for outflow of hot waste gases of combustion while said one gun flue is operable for inflow of rich fuel'gas to its set of vertical flues and the other of the two gun flues is then idle to flow of rich fuel gas to its set of vertical flues, the other of said waste gas'recirculation ducts vconnecting the other of said gun ,flues with a regenerator, which regenerator is operable for inflow of air while said other gun flue is idle to flow of 'richf fuel gas to its set of vertical flues and said one of .the two gas gun flues is in operation for inflow of rich fuel gas to its vertical combustion flues, and which regenerator is operable for outflow of hot waste gases of combustion while said other gun flue is operable for inflow of rich fuel gas to its set of vertical combustion flues and said one of the two gun flues is then idle to flow of rich fuel gas to its vertical flues and means for introducing rich fuel gas in the form of a jet into the ends of the gun flues at the region of juncture of the waste gas recirculation duct therewith.

each having a regenerator air inlet port at its bottom 7 for inflow ofregeneratively preheated air a regenerator and for outflow of waste gases of'comybustion from the flue to said regenerator, a pair of horizontal rich fuel gas gun flues operable in alternation with each other for inflow of rich fuel gas, said gun flues extending lengthwise of the heating wall at the bottom of said flues, with rich fuel gas riser ducts leading from one of the two gun flues to the bottoms of the flues of one set, and with rich fuel gas riser ducts, leading from the other of the two gun flues .tothe bottoms of the flues of-the other set, a waste gas recirculation duct at nation with the on and oif operation of the other gun flue.

' 3. In a coking retort oven, a horizontal heating wall constituted of two sets of vertical combustion flues each operable in alternation with the other for upflow comfbustion and downflow of combustion products, said flues each having .a regenerator air inlet port at its bottom for inflow of regeneratively preheated air-thereto from,

a regenerator and for outflow of waste, gases of combustion from the flue to said regenerator, a pair of horizontal rich fuelgas gun flues operable in alternation with each other for inflow of rich fuel gas, said gun flues extending lengthwise of the heating wall .at'the bottom of said flues, with rich fuel gas riser ducts leading from one of the two gun flues to the bottoms of the flues of.

one set, and with rich fuel gas riser ducts leading from :the other of the two gun flues to the bottoms of the flues of the other set, a waste gas recirculation duct at each of the opposite ends of the horizontal heating walls, each of said ducts connecting one of the gun flues with a regenerator in communication through the aforesaid regenerator air inlet ports with the vertical combustion flues with which the other gun flue is communicably connected by the aforesaid rich fuel gas riser. ducts, and means for introducing rich gas in the form of a jet into the ends of the gun flues at the region of juncture of the waste gas recirculation duct therewith.

4. In a h-orizontal'gas gun flue coke oven batterycornprising: a series of alternate horizontal coking retort oven chambers and intermediate heating walls arranged side by side in a row, each heating wall comprising in- ;terior and exterior groups of flues in end to end relation along the heating wall and co-mmunicably connected at their tops for upflow combustion and downflow of combustion products in alternation; regenerators sepaing walls and commnnicably connecting the regenerators.

of one set with the pusher side exterior group-s and coke side interior groups of flues in the, alternate heating walls, and with the pusher side interior groups and coke side 'exterior groups of the intermediate heating walls; re-

generator ducts in the base of the heating walls and comthereto from r municably connecting the regenerators of the other set with the pusher side exterior groups and coke side interior groups of heating flues of the intermediate heating walls and with the pusher side interior groups and coke side exterior groups ofheating fluesof the alternate heating walls; a gas gun flue extending inwardly of each heating wall from the pusher side of the battery, with each gun flue extending along the pillar walls for the heating wall in the region of the bottoms for the 10 heating flues to the coke side of the battery, each such gas gun flue being provided with a gas gun inlet for rich fuel gas on the pusher side of the battery and being connected by rich gas riser ducts with thebottoms of the vertical heating flues of the pusher side interior group and coke side exterior group of flues of its heating wall; a second gas gun flue extending inwardly of each heating wall fromthe coke side of the battery, with each gun flue extending along the pillar wall for the heating wall in the 'region'of the bottoms for the heating flues to the pusher side of the, battery, each such gas gun flue being .provided with'a gas gun inlet for rich fuel gas on the coke side of the battery and being connected by rich gas riser ducts with the bottoms of the vertical heating flues of the coke side interior group and pusher side'exterior group of flues of its heating wall; the regenerators of said one set and the pusher side gas gun inlets for the gas gun flues for alternate heating walls and coke side gas gun inlets for the ga-s'jgun flues for the'inter mediate heating walls, being operable in alternation with the regenerators of the other set and the pusher side gas gun inlets for the, gas gun flues for the intermediate heating walls and coke side gas gun inlets for the gas gun flues for the alternate heating walls, for inflow combustion in, and outflow of combustion products from, the vertical flues of the groups that they serve as aforesaid, ,whereby all portionsof the coal masses in-the coking chambers may be concurrently heated'by flame heating on each side part and waste gas heating on eachof the opposite'side parts in alternation 40 with each reversal in operation of the flues and regenerators incorrespondence with the reversal in operation ofgthe regenerators,'a waste gas recirculation duct at each of the opposite endsof the heating walls, each of said ducts at opposite ends of a heating wall communi- 5 cably' connecting one of the gun flues in its heating wall with the top of a regenerator in communication-with the vertical heating flues with'whic-h'the other gun flue is communicably connected by the aforesaid rich gas riser ducts. i

References Cited by therExaminer I UNITED STATES PATENTS 1,678,803 7/28 Van Ackeren 202-141 1,704,239 3/29 Becker 202-441 2,043,945 v6/36 Beirnann 202141 2,507,554, 5/50 Van Ackeren 202151 2,515,815 7/50 Willputte 202141 x 2,516,929 .8/50 Van Ack'eren- 202-151 3,123,540 3/64 Van Ackeren 202--141 MORRIS ,O. WOLK, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner. 

2. IN A COKING RETORT OVEN, A HORIZONTAL HEATING WALL CONSTITUTED OF TWO SETS OF VERTICAL COMBUSTION FLUES EACH OPERABLE IN ALTERNATION WITH THE OTHER FOR UPFLOW COMBUSTION AND DOWNFLOW OF COMBUSTION PRODUCTS, SAID FLUES EACH HAVING A REGENERATOR AIR INLET PORT AT ITS BOTTOM FOR INFLOW OF REGENERATIVELY PREHEATED AIR THERETO FROM A REGENERATOR AND FOR OUTFLOW OF WASTE GASES OF COMBUSTION FROM THE FLUE TO SAID REGENERATOR, A PAIR OF HORIZONTAL RICH FUEL GAS GUN FLUES OPERABLE IN ALTERNATION WITH EACH OTHER FOR INFLOW OF RICH FUEL GAS, SAID GUN FLUES EXTENDING LENGTHWISE OF THE HEATING WALL AT THE BOTTOM OF SAID FLUES, WITH RICH FUEL GAS RISER DUCTS LEADING FROM ONE OF THE TWO GUN FLUES TO THE BOTTOM OF THE FLUES OF ONE SET, AND WITH RICH GAS RISER DUCTS LEADING FROM THE OTHER OF THE TWO GUN FLUES TO THE BOTTOMS OF THE FLUES OF THE OTHER SET, A WASTE GAS RECIRCULATION DUCT AT EACH OF THE OPPOSITE ENDS OF THE HORIZONTAL HEATING WALLS, SAID WASTE GAS RECIRCULATION DUCTS CONNECTING EACH ONE OF THE GUN FLUES WITH A REGENERATOR, ONE FLUE WITH A REGENERATOR OPERABLE FOR INFLOW OF AIR AND OUTFLOW OF WASTE GAS IN ALTERNATION WITH THE OFF AND ON OPERATION OF THE GUN FLUE, AND THE OTHER FLUE WITH A DIFFERENT REGENERATOR OPERABLE FOR OUTFLOW OF WASTE GAS AND AIR INFLOW IN ALTERNATION WITH THE ON AND OFF OPERATION OF THE OTHER GUN FLUE. 